clang-format: Improve c-style cast detection.

Before:
  #define x ((int) - 1)
  #define p(q) ((int *) & q)
After:
  #define x ((int)-1)
  #define p(q) ((int *)&q)

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@186324 91177308-0d34-0410-b5e6-96231b3b80d8